Strange vacuum issue

[Funnyman141]

Well after playing with the 87 we have found a strange issue, we hooked the vacuum gauge up to one of the empty vacuum ports on the intake, at idle it was sitting around 20 hg but as we revved it up the vacuum raised to about 25-28 hg. Isn't it supposed to drop the higher you rev?
Also the O2 sensors readings are jumping from .025 volts to .863 volts at idle, when you rev the motor up it stays in between .247 to .638 I know that is better but isn't it supposed to be closer to .4 volts?

Thanks for your help!

 

[--weezl--]

not sure about your o2 thing, but your vacuum can increase if you only crack the throttle slightly, as the motor turns faster, and sucks harder, but the throttle plate is still restricting almost as much as it was fully closed? not sure if that's true or not, but it makes sense to me...

 

[Mark_88]

Yeah, I think the vacuum increases with higher rpm...but my guage did something similar when I did a WOT check...at some point, the vacuum is what opens the EGR valve so it would make sense that vacuum increases with gradual increases in rpms...

Also not sure about the O2 sensor...don't have one on my truck...but it may be normal...since the alternator is going to be spinning faster...or it could mean your voltage regulator is not doing what it's supposed to do...

 

[--weezl--]

mark, i think you're thinking of it backwards, the vacuum doesn't open it, or it does... i forget... when you hit the throttle, your vac drops, which "turns off" the egr (closes?)

funnyman, think about it this way, the higher RPM, the more demand for air there will be, and thus the higher vacuum, however, the more you open the throttle plate, the more supply there is, so as a result, the vacuum drops also... it's kinda a ballancing act... so if you redline the motor, then let off the gas, fully, your vac will be through the roof

 

[Mark_88]

mark, i think you're thinking of it backwards, the vacuum doesn't open it, or it does... i forget... when you hit the throttle, your vac drops, which "turns off" the egr (closes?)

This is an 87 FI I take it...so it could be strictly vacuum controlled...

I found this info...

[FONT=arial, Arial, Helvetica]However at cruise the Fuel/Air mixture is set as lean as possible for maximum economy and this in turn generates the highest temperatures, and so the EEC-V uses these conditions to inject exhaust gas into the inlet manifolds to reduce emissions. Older vehicles used vacuum devices to control the EGR valve whereas the Scorpio uses the EEC-V and it's sensors to control it.

There's more info here...[/FONT]http://www.fordscorpio.co.uk/egr.htm

Not sure if that's relevant to the situation though...

 

[Funnyman141]

Well when I did the vacuum test I did hit WOT but it still stayed around 25-28 hg when I let it off thats when I got high numbers but I already knew that would happen. lol
Also my E.G.R. valve was blocked off due to it being a huge vacuum leak.

 

[--weezl--]

no idea then man... sorry

 

[Earl43P]

http://www.therangerstation.com/Magazine/Summer2003/VacuumLeaks.htm